Since a method for the synthesis of a large amount of C60 was established in 1990, extensive studies have been made of fullerene. As a result, numerous fullerene derivatives have been synthesized and their various functions have been made obvious. With this technical progress, the development of various uses of electronic conductor, semiconductor, bioactive material, etc. comprising fullerene derivatives has been under way (for general remarks, see “Gendai Kagaku (Modern Chemistry)”, April 1992, page 12, and June 2000, page 46, Chem. Rev., 1998, 98, 2527, etc.).
The inventors have synthesized various fullerene compounds comprising ten organic groups connected to the fullerene skeleton (hereinafter occasionally referred to as “derivative bearing 10 attached organic groups” or “10-fold adduct”) and various fullerene compounds comprising five organic groups connected to the fullerene skeleton (hereinafter occasionally referred to as “derivative bearing 5 attached organic groups” or “5-fold adduct”) and reported them (see Japanese Patent Laid-Open No. 1998-167994, Japanese Patent Laid-Open No. 1999-255509, Japanese Patent Laid-Open No. 2002-241323, J. Am. Chem. Soc. 1996, 118, 12850, Org. Lett. 2000, 2, 1919, Chem. Lett. 2000, 1098). The inventors have also synthesized fullerene compounds comprising three organic groups connected to the fullerene skeleton (hereinafter occasionally referred to as “derivative bearing 3 attached organic groups” or “3-fold adduct”) and reported these compounds, including their metal complexes, separately of the aforementioned fullerene compounds (see Japanese Patent Laid-Open No. 1999-255508, J. Am. Chem. Soc. 1998, 120, 8285, Org. Lett. 2000, 2, 1919.).
In order to apply fullerene derivatives to various purposes, it is extremely useful to render them soluble in an organic solvent. It is thought that a fullerene derivative having a high solubility in an organic solvent, if obtained, can be applied to uses requiring dissolution in an organic solvent such as intermediate which is subjected to further transformation to synthesize other derivatives, electronic industrial material and ligand of metal complex, making it possible to drastically expand the application of fullerene derivatives.
However, all various known fullerene derivatives, including those disclosed in the above cited references, have an extremely low solubility in an ordinary organic solvent having a relatively small polarity. It is thus disadvantageous in that the solvent applicable when these fullerene derivatives are applied to the aforementioned various purposes is restricted, making the application of these fullerene derivatives extremely difficult or substantially impossible. Under these circumstances, a fullerene derivative having a high solubility in an organic solvent has been desired.